CHAPTER 1: INTRODUCTION
Page 1-10
EMME USER’S GUIDE
1.3
REPEATER FUNCTIONALITY
The EMME’s repeater functionality ensures that any problem segments
connected to any port on the MMAC-FNB will not affect any other
segments connected to the MMAC-FNB. For example, if 32 consecutive
collisions are detected on any segment, or if a collision detector is on for
more than 2.4 milliseconds, the EMME automatically partitions that
segment from the MMAC-FNB. The segment is automatically
reconnected to the MMAC-FNB when a good packet is transmitted onto
the segment.
For Cabletron Systems’ original non-repeater MIMs (i.e., TPMIM,
FOMIM) the EMME’s IEEE 802.3 compliant repeater provides the
MMAC-FNB with the ability to achieve maximum data paths on all
Ethernet transmission media, including 10BASE-T twisted pair, fiber
optic, and thick or thin Ethernet type cabling. To attain these maximum
data paths, the EMME retimes data packets and regenerates the preamble
of each data packet that enters the MMAC-FNB.
With the Cabletron Systems repeater modules (TPRMIM, CXRMIM, and
FORMIM), packets are repeated autonomously on the MIM and are not
channelled through the EMME. Module to module repeating is achieved
over the FNB backplane. The EMME provides management for these
modules and keeps Device, Network, Board, and Port Level performance
and error statistics.
1.4
BRIDGING FUNCTIONALITY
The EMME automatically configures itself as a bridge between channels
A, B, C, and D, for a four port bridge maximum. The EMME provides
802.1d compliant bridging capabilities to prevent unnecessary network
traffic from passing between segments.
Frames received by the EMME are forwarded to four megabytes of
buffering memory. The EMME’s processor accesses the frames from the
buffered memory and passes address information to the bridging
algorithm. Then, based on the bridging decision, the frames are filtered or
forwarded.
The EMME incorporates the Spanning Tree and DEC Spanning Tree
Algorithms that allow network architects to set up bridges in parallel
between segments as backup paths for fault tolerance. These bridges
remain in a standby condition until the primary parallel path fails.
